A wide variety of soap bar compositions and manufacturing processes are known in the art. Commonly, soap bar compositions for toiletry purposes are milled soaps of low moisture content (from about 5% to about 18% water) based on a mixture of tallow and coconut oil feedstocks. Bars having milled soap characteristics can also be prepared from soap of a high moisture content, as described for example in U.S. Pat. No. 2,686,761 and U.S. Pat. No. 2,970,116 by mechanically working the soap at a temperature of from about 80.degree. F. to 125.degree. F. and by using an appropriate fat feedstock. Such a process has two main advantages; firstly, it is relatively energy-efficient in that less drying of the neat-kettle soap is required; and secondly, it produces soap bars having desirable translucency or transparency as a result of beta-phase soap formation.
From the consumer acceptance viewpoint, of course, the lathering and mildness characteristics of a toilet bar composition are highly important and there is a continuing need to improve these areas of performance. Traditionally, lather enhancement has been achieved in two ways. Firstly, shorter chain fatty acid soaps such as coconut soaps are known to produce a much richer lather than longer chain fatty acid soaps such as those based on tallow and it is therefore common practice in toilet bar manufacture to add up to 50% coconut soap to the tallow fat feedstock. Secondly, superfatting agents such as coconut fatty acid also improve the volume and richness of the lather when added to toilet bars in levels of up to about 10%. At higher levels, however, coconut soaps increasingly have a detrimental effect on bar mildness while fatty acids can produce undesirable softening of the bar. Moreover, coconut soaps and fatty acids are both expensive commodities and it would therefore be desirable to achieve improvements in lathering without recourse to high levels of these ingredients.
In the case of beta-phase soaps, moreover, there is a more fundamental difficulty in achieving high lathering through the use of coconut soaps and superfatting agents. Fat feedstocks which are relatively rich in shorter chain (less than 16 carbon atoms) saturated fatty acids inhibit the formation of beta-phase soap and are therefore unsuitable for making transparent or translucent soap bars. In a similar way, beta-phase soap formation is also inhibited by the addition of free fatty acid superfatting agents in levels above about 1%-3%.
EP-A-0222525 in the name of the present Applicant addresses the problem of improving the lathering characteristics of beta-phase toilet bar compositions and advocates the incorporation of certain water-soluble polymer materials for this purpose. A major draw-back of these polymer additives, however, is their tendency to promote formation of scum under hard water conditions, an effect which is particularly noticeable and undesirable when the toilet compositions are used during bathing. While EP-A-0222525 generally recognise this problem and teaches the value of synthetic surfactants for controlling scum formation, nevertheless, one specific class of surfactant material has now been identified which is almost uniquely effective in its ability to control scum, which simultaneously provides benefits in other areas of bar performance, notably reduced smear characteristics and improved processing and stamping, and which at the same time allows for excellent lathering, mildness and beta-phase soap (transparency/translucency) characteristics.